The present Invention is a rotary power transmission device providing an automatic and continuous, i. e., stepless, variation of input to output speed ratio in response to both demand speed and demand torque, particularly as required in vehicular applications. It is very desirable in such applications to maintain constant input speed and torque (power) of the prime mover as output speed and torque vary due to operator demand or to changing environmental conditions such as vehicle inclination, wind loading, or other external resisting forces. In the case of an engine driven vehicle, use of such a transmission can allow engine speed to be maintained at its most fuel-efficient operating point. For a human-powered vehicle, use of such a transmission can allow the operator to supply a comfortably maintainable power input while navigating hills, rough terrain, etc.
The present Invention allows this optimum matching of input to output power to be accomplished both continuously and automatically. Its basic operating principle is that of the well-known friction wheel and plate transmission, but improves upon such devices by constraining the wheel between two counter-rotating drive plates, both plates supplying torque input, with wheel being the output, and with no idler wheel or other intermediate device being used. With two diametrically opposite tangential contact interfaces rather than a single interface, this design causes the tractive forces applied to wheel to be balanced under high loading without undesired deflection of components, as is the tendency with a single tangential interface design. Enabling high loading at these contact points obviates another disadvantage of friction transmissions of the prior art, namely, slippage between drive and driven members due to the inability of prior designs to maintain adequate interfacial friction forces.
Certain continuously variable transmissions of the prior art attempt to control ratio as a function of either torque or speed, but not a combination of these. The present Invention improves upon the prior art by providing a novel and useful means of combining these variables in the following way. Traction wheel is moved and positioned upon drive plates by force imposed by a fluid actuated piston, the actuating pressure of which is modulated by combined action of pump speed and disposition of a flow control valve. By causing pump speed to be proportional to demand speed, and by causing the restriction of flow control valve to be defined by an environmental variable such as vehicle inclination, the combined effect is a continuous modulation of system pressure and thus speed ratio as a function of both demand speed and demand torque, as further described below.
Alternately, the present Invention allows for use of a manual flow control valve in parallel with said automatic valve, enabling, for example, the operator of a powered vehicle equipped with the transmission to manually modulate vehicle speed ratio range during operation.
Additionally, the present Invention improves upon the prior art by equipping traction wheel with rollers, constrained to and circumferentially distributed upon the wheel, which enable wheel to translate via rolling motion upon the drive plates while wheel is under high contact loading imposed by the drive plates, the wheel concurrently transmitting torque from drive plates to output shaft.
The object of the present Invention is to provide a rotary power transmission able to perform a continuous, i. e., stepless, variation of output to input speed ratio, and to perform this variation automatically in response to both demand speed and torque. This object is accomplished by a hydraulic control means which utilizes the combined action of a pump responsive to demand speed, and a flow control valve responsive to an environmental variable such as inclination.
Further object is to obtain, by use of the transmission within a vehicle or other powered device, improved efficiency by enabling the prime mover to maintain an optimum speed under a wide range of operating conditions.
Further object is to provide a continuously variable transmission having improved power transmitting capacity by providing an output traction wheel in concurrent tangential enforced contact with two counter-rotating drive plates, said design enabling generation of high tractive forces while balancing said forces without undesirable deflection of components.
Further object is to provide an improved mechanism for actuating continuous speed ratio variation with minimum internal effort while maintaining high tractive forces, specifically by use of rollers mounted upon traction wheel which enable said wheel to translate upon said drive plates via rolling action under high forces while maintaining output torque traction.